1. Field of the Invention
The present invention relates to an ink jet recording apparatus which discharges inks to a recording medium to execute recording, and more particularly to a preliminary discharge control technology.
2. Description of the Related Art
There is a recording apparatus which includes functions of a printer, a copying machine, and a facsimile, or a recording apparatus which is used as an output device for a complex electronic device including a computer and a word processor, or a work station. Such a recording apparatus is configured to record images (including characters) on a recording medium such as a sheet or a plastic sheet based on image information (including character information). With respect to a recording method, the recording apparatus can be classified into an ink jet type, a wire dot type, a thermal type, a laser beam type and the like. Among such recording types, the recording apparatus of the ink jet type (i.e., ink jet recording apparatus) discharges inks from a recording unit (i.e., recording head) to a recording medium to perform recording. As compared with the other recording types, the ink jet recording apparatus has advantages in that high definition can be achieved more easily and the apparatus can be operated silently and at a higher speed. Moreover, its selling price has decreased in recent years. To increase a recording speed, the ink jet recording apparatus uses a recording head integrating a plurality of ink discharge ports as ink discharge portions and a plurality of liquid paths for a recording head in which a plurality of recording elements is integrated and arrayed. The ink jet recording apparatus generally includes a plurality of recording heads to make a color print.
When no recording is performed, the recording apparatus stands by in a home position of the recording head while the discharge ports of the recording head is covered with a cap to suppress ink evaporation. If this stand-by state of no recording continues for a long time, the ink evaporates gradually from the discharge port which causes thickening of ink, resulting in an increase in ink concentration, or defective discharge. To reduce such an effect, preliminary discharge that is not used for recording, or suction of ink from the discharge ports is carried out as recovery work of the recording head before starting recording, in order to remove thickened inks. For example, Japanese Patent Application laid-Open No. 3531347 discusses a configuration for calculating ink viscosity based on a remaining amount of ink so that preliminary discharge conditions can be changed.
Furthermore, a wiping operation can be performed to remove inks stuck on a face of the recording head where the discharge ports are arranged side by side. The sticking of ink is caused by spattering of the inks from the recording medium during a recording operation. After suction is completed, a wiping operation is carried out to remove inks stuck on the face of the recording head where the discharge ports are arranged side by side. Preliminary discharge that is not used for recording is carried out in the wiping operation to remove inks pushed into the discharge ports. Moreover, when inks of a plurality of different colors are sucked by the same cap, mixed color inks generated in the cap which has sucked the inks, enter the discharge ports. To remove the mixed color inks which have entered the discharge ports, preliminary discharge that is not used for recording is carried out after the suction is completed.
When discharge systems are operated in the ink jet recording apparatus, the discharge is accompanied by heat of some kind. There is a case where the heat is generated to discharge inks, in other words, inks are discharged using heat energy. A representative example of an ink jet recording apparatus which operates based on ink discharge using heat energy is a recording apparatus in which bubbles are rapidly generated by film boiling to discharge inks. The film boiling occurs in inks due to heat energy generated by a heating element serving as a discharge energy generation element. As a discharge system which incidentally generates heat, as discussed in Japanese Patent Application Laid-Open No. 3531347, for example, a system that uses a well-known piezoelectric element as discharge energy generation element is available. According to this system, heat is indirectly generated due to vibration of the piezoelectric element although no direct heat is generated to discharge inks.
However, in the ink jet recording apparatus, in order to achieve higher image quality and a higher speed, the amount of each discharge is reduced to increase a recording pixel density, or the longer recording head is utilized to increase the number of discharge ports. As a result, heat energy applied to the recording head during the preliminary discharge operation is increased, which can cause an increase in temperature of the recording head.
Further, if a heat sink disposed in the recording head is removed to reduce its manufacturing cost, a temperature of the recording head can be further increased. When there is enough ink in an ink tank for recording, ink is supplied adequately to the recording head. In such a case, heat applied to the recording head for preliminary discharge is discharged to the outside together with the discharged ink. However, when a remaining amount of ink in the ink tank becomes small or ink runs short, heat cannot be effectively discharged from the recording head when preliminary discharge is executed in a state that the ink used for recording is insufficient. Thus, a temperature of the recording head may increase more rapidly. As a result, a function for protecting the recording head and a recording operation can be restrained, against user's intension.